Eady instability of isolated baroclinic jets with meridionally varying tropopause height

Song, YC Nakamura, N

Yc. Song et N. Nakamura, Eady instability of isolated baroclinic jets with meridionally varying tropopause height, J ATMOS SCI, 57(1), 2000, pp. 46-65

67

INGLESE

Article

Earth Sciences

JOURNAL OF THE ATMOSPHERIC SCIENCES

0022-4928 → ACNP

57

1

2000

46 - 65

ISI

0022-4928(20000101)57:1<46:EIOIBJ>2.0.ZU;2-P

An efficient solution procedure is developed for a nonseparable semigeostro phic Eady problem an a semiinfinite f plane. A model is designed to study t he effects of meridionally isolated jets and tropopause morphology on baroc linic instability. Potential vorticity (PV) is assumed to be piecewise cons tant and discontinuous at the tropopause, whose height is allowed to vary w ith latitude. The computational domain is discretized in a stretched coordi nate to maintain adequate resolution in the vicinity of the tropopause and axis of the jet. The basic state is numerically inverted from the two PV va lues with the specification of only the meridional profiles of potential te mperature (PT) at the surface and (unspecified) tropopause height. The nons eparable eigenvalue problem about this basic state is solved for the discre te (zero-PV) normal modes. Since continuum modes are not sought, the size o f the problem is reduced greatly, keeping the storage and CPU requirements moderate even at relatively high spatial resolutions. This model is used to investigate changes in the zonal-mean state and the s tability thereof, in response to arrangements of the zonal-mean PT at the s urface and tropopause. In particular, (a) partial mixing of surface PT and (b) appearance of a local minimum of PT on the tropopause are considered as models of baroclinic adjustment and tropopause folds, respectively. The fo rmer renders the mean flow more barotropic and shifts up the zonal scale of baroclinic instability. The latter gives rise to a markedly dipped tropopa use that is barotropically unstable at various ranges of wavenumbers. The r esults' implications on the life cycle simulations and roll-up of stratosph eric intrusions are discussed.